1. Field of the Invention
The invention relates to a valve unit for interrupting or releasing a flow of a pressurized medium along a hollow duct. Furthermore, the invention relates to the use of the valve unit in a dosing system for the metered discharge of the medium from a cartridge-needle configuration, whose cartridge is connected to the needle configuration via at least one hollow duct and has an open cartridge end, to which a pressurizing means is applied, which drives the medium in the cartridge in the direction of the needle configuration.
2. Description of the Prior Art
Devices according to the metered discharge of viscous media, preferably low, moderate, and high viscosity liquids, such as oils, greases, glues, and soldering pastes, to name only a few, which are also known in manifold forms under the title “dispenser”, are used in greatly varying technical fields, such as precision engineering, nanotechnology, and microtechnology, and in particular areas of microelectronics, micro-optics, and micro-mechanics, and also in biotechnology and medical technology. Typical applications of dispenser systems of this type for moderate and high viscosity media relate, for example, to the exact discharge and positioning of extremely small adhesive droplets for joining in electronics manufacturing, the lubrication of bearings using oils and greases in mechanical engineering, preferably in the fields of micromechanics, and the continuous or cyclic delivery of reagents in the chemical industry or for purposes of analytical technology or also for administering extremely finely dosed liquid pharmaceuticals for patient care, in particular in intensive care.
An overview of available dispenser systems on the market for moderate and high viscosity media may be inferred from the article by F. Kohler Point for Point—the Technologies for the Dispensing of Soldering Pastes, published in “Productronic” (1991), issue 4, pages 18 through 20, which are particularly capable of generating and placing droplets, so-called dots, in the context of cyclic dispensing of media. For this purpose, differentiation between the following systems is required:
a) Time/Pressure Cartridge Dosing System
This system may be understood as the basic system, which is also used in identical or altered form in the dispenser systems explained briefly hereafter for the dosed provision of viscous media. The dispenser system identified as the basic system comprises a cartridge having a dispenser needle on the lower end and a pressure connection on the upper end of the cartridge. Via targeted pressure buildup in the upper end of the cartridge, a piston unit is pressed against the remaining cartridge volume, in which the viscous medium to be dispensed is located for discharge through the dosing needle. Cartridge/dispenser needle units are available as disposable articles and are to have a corresponding pressure attachment removably fixed.
b) Rotation-Screw Dosing Systems
So-called rotation-screw dosing systems provide a rotation screw, which may usually be driven via a geared motor, which is used as the delivery screw for the viscous medium to be discharged and is situated axially to the dispenser needle. The viscous medium to be dispensed is supplied longitudinally to the delivery screw at low pressure, for example, employing the time/pressure cartridge dosing system previously identified. Depending on the rotational velocity of the delivery screw implemented as the rotation screw, the volume flow of viscous medium discharged through the needle unit may be set to be extremely finely dosed.
c) Peristaltic Dispenser
A cartridge filled with viscous medium is again used for the targeted discharge of the medium at low pressure into a plastic tube, which provides two closable tube ends. If a closure is opened on one end, the media may flow out of the cartridge into the tube. The first closure is then closed and the second closure is accordingly opened, a plunger provided between the two closures acts on the tube to deliver the viscous medium through the second opening into a corresponding dispenser needle.
d) Piston Positive Displacement Dosing Systems
So-called piston positive displacement dosing systems typically have a cartridge filled with viscous medium, which conducts the medium at low pressure through a channel to a pump chamber, along which a piston is situated so it is movable, which generates a partial vacuum inside the pump chamber upon movement upward, by which the viscous material flows out of the cartridge into the pump chamber. When the piston moves downward, the material feed along the cartridge is interrupted and the piston presses the desired quantity of the medium out through a corresponding dispenser needle, which is situated axially from the pump chamber.
Dispenser systems briefly outlined above are fundamentally capable of discharging viscous media volume-dosed to local areas which may be predefined, but limits are set on the precision in regard to extremely small volume deliveries and the high-precision reproducibility of the delivered volume quantity in relation to the total emptying of a cartridge filled with viscous medium. The described dispenser systems and the use of cartridges thus offer a poor volume repetition precision, that is, the volumes of individual dots applied in sequence increasingly vary, particularly because on the one hand the viscosity of the material changes as a result of variations of humidity and temperature, and a corresponding change of the pressure value is accordingly necessary to dispense an equal volume. On the other hand, a change of the dispensed volume occurs if the same pressure is applied to the full cartridge as to the nearly empty cartridge. Thus, for example, the volume discharge from a cartridge at constant delivery pressure changes by up to 19% if a 10 cm3 cartridge is used.
The above problems may be technically managed best using the piston positive displacement system identified in d), but systems of this type have the most complex designs and are thus the most costly. The dosing systems identified above also reach functional limits when attempting to miniaturize systems of this type.
In addition, known dispenser systems tend to drip upon lifting of the dosing needle after each material discharge, because the overpressure necessary along the dosing needle for the material discharge is not dissipated or is not dissipated in a timely enough manner.
Time-pressure cartridge dosing systems, as previously noted, are also known in which a switchable valve, which operates on an electromagnetic or piezoelectric basis and requires electrical current for activation, which finally results in heating of the system which interferes with an exact media discharge, in particular if extremely small material quantities in the nanometer range are administered, between the cartridge storing the medium to be dispensed and the needle configuration. In addition, switchable flow valve systems of this type usually have large installation sizes, because of which integration and in particular application in micro-dosing systems is only possible in a restricted way. Furthermore, the closing procedure results in a temporary pressure buildup inside the needle in valves known per se because of the design, which results in dripping, which is to be avoided. In addition, flow valve systems known up to this point are either suitable for flow interruption of gaseous media or for liquid media. A valve system which is capable of controlling media having either liquid or gaseous aggregate state is currently not known. Finally, the production costs connected with the known valves are significant.
The device described in DE 2839774 A1 for setting the flow cross-section of a valve is based on a permanent magnet, held via an axial thread, being set in rotation uniformly by pivoting an annular magnet radially enclosing the permanent magnet, by which the internal permanent magnet may be axially positioned by the thread guide. The internal permanent magnet is connected to a conical pin, which is capable of closing a valve opening as a function of the axial position of the permanent magnet.
DE 38 02 658 A1 describes a solenoid valve whose mode of operation is determined by the axial position of a permanent magnet mounted so it is axially movable to the hollow duct. Because of the magnetic conditions of the permanent magnets present in the solenoid valve, the valve configuration remains open in a basic position unloaded by external force actions, particularly because the axially movable magnet unit experiences an axially acting repelling force due to the magnet unit also being provided in the hollow duct. In contrast, if a corresponding axially acting flow pressure or volume flow V acts on the valve seat 3, it is axially displaced and moved against a valve needle until a maximum volume flow transfers the valve unit into a closed state. Due to the shaping of the valve body and the desired significant longitudinal mobility of the valve seat in the axial direction, the known solenoid valve may especially advantageously be used as a magnetic regulating valve. Optical sensors are provided for this purpose along the cavity wall to detect the axial position of the valve seat.